So when would you pronounce a lax consonant as a tense one? The whole idea of this kind of phonetic change is to make the pronunciation more natural, and if you ask a native speaker, most probably they would simply tell you “When it sounds more natural that way.” Fortunately, a lot of tensing occur with a regular rule, as follows:

When a consonant ㅂ ㅈ ㄷ ㄱ or ㅅ follows another consonant other than the nasal (ㄴ ㅁ ㅇ) or ㄹ, you need to pronounce it as ㅃ ㅉ ㄸ ㄲ or ㅆ (i.e. tensing).

Examples

As you can see from the last example, this tensing process can apply across word boundary, depending on the focus of the phrase or sentence.

Tensing without a Rule

While we have a regular rule for tensing, unfortunately there are many other Korean words which tensing applies without a rule. You will need to learn them on a case-by-case basis down the road of your Korean learning career.

In the first 3 examples, you can see that different meanings in the same word are distinguished by with or without tensing in the second hangul. The last 2 examples is to demonstrate that the pattern with future tense modifier …을 거 is always tense but not the pattern with present/past tense modifier 는/은 거.

A lot of borrowed words have an optional tensing in the initial consonant, such as
바스 [바스 or 빠스] for bus, 바나나 [바나나 or 빠나나] for banana, or 게임 [게임 or 께임] for game. For native Korean words, very often tensing for the initial consonant is to emphasize intensity, such as 작아요 [짜가요] to emphasize it is small.